Causes of Birth Defects

Transcription

1 Causes of Birth Defects

2 Some medical / genetic terms: congenital defects: visible defects present at birth (due to any cause (genetic, developmental error ). syndrome: the symptoms that characterize any abnormal condition (due to genetics, development, chronic injury, etc.). pleiotropy: refers to the multiple structures effected by one gene or one mutant gene. Haploinsufficiency occurs when a diploid organism only has a single functional copy of a gene (with the other copy inactivated by mutation) and the single functional copy of the gene does not produce enough of a gene product (typically a protein) to bring about a wild-type condition, leading to an abnormal or diseased state. It is responsible for some but not all autosomal dominant disorders.

7 Other birth defect genes can be identified with prior knowledge as in similar defects seen in animal models candidate gene mapping Animal model systems of diseases

8 Waardenburg Syndrome Very pale or brilliantly blue eyes, eyes of two different colors (complete heterochromia), or eyes with one iris having two different colours (sectoral heterochromia); A forelock of white hair (poliosis), or premature graying of the hair; Wide-set eyes (hypertelorism) due to a prominent, broad nasal root (dystopia canthorum particularly associated with type I); Moderate to profound hearing impairment (higher frequency associated with type II); and A low hairline and eyebrows that touch in the middle. Patches of white pigmentation on the skin have been observed in some people. Sometimes, abnormalities of the arms, associated with type III, have been observed. Pax3 or Mitf heterozygotes

20 Endocrine disruptors A large number of drugs, environmental chemicals either mimic or interfere with hormones. ex.: Diethylstilbestrol (DES) s-60 s, prescribed to pregnant women to prevent premature labor and miscarriage -- Found to damage female reproductive system, cause abnormal development of male reproductive system. -- Now banned, major example of an environmental estrogen Environmental estrogens are a major class of chemicals that mimic estrogen-- Now a HUGE area of research and friction with plastics and pesticides industry

23 Bisphenol A (BPA): First made as a synthetic estrogen. Later found to be useful component in plastics. Common in polycarbonate plastics (until recently: Nalgene) (soda containors, baby bottles, toys.) Many documented effects on gender development in lab animals. Causes Chromosome non-disjunctions during meiosis (trisomies)

24 Effects of BPA (measured in studies of mice or rats) Dose (µg/kg/day) "Permanent changes to genital tract" "Changes in breast tissue that predispose cells to hormones and carcinogens" 2 "increased prostate weight 30%" 2 "lower bodyweight, increase of anogenital distance in both genders, signs of early puberty and longer estrus." 2.4 "Decline in testicular testosterone" 2.5 "Breast cells predisposed to cancer" 10 "Prostate cells more sensitive to hormones and cancer" 10 "Decreased maternal behaviors" 30 "Reversed the normal sex differences in brain structure and behavior" 50 U.S. human exposure limit (not a result from an animal study, but a guideline set by EPA)

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